Abstract
The efficacy of natural enemies in controlling pests under field conditions is largely correlated with their capacity to spread within infested crops. In this study the spatial dispersal of the California red scale parasitoid Aphytis melinus DeBach (Hymenoptera: Aphelinidae) was evaluated in the field after augmentative releases. The experiment was conducted in 2007 in six 1-ha plots in a Sicilian citrus orchard under integrated pest management. A total of 180,000 A. melinus adults was released in each of three plots and the other plots were left as untreated control. The flight range of the parasitoid was evaluated, for 35 days after the release, on 16 trees per each plot, located at 20 and 40 m from the central release point using yellow sticky traps activated with Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) sexual pheromone and by monitoring the percentage parasitism of the scale on fruits and twigs. The effects of the distance from the release point and density of susceptible stages of host on parasitoid dispersal were evaluated. The number of wasps captured during the whole trial was greater in the traps located 20 m from the release point than in those at 40 m and in the control plots. Aphytis melinus dispersed over distances less than 40 m based on both the lower per- centage parasitism and numbers captured recorded at distances of 40 m. The results are discussed in the context of the biological control of California red scale in citrus orchards by means of wasp releases. In particular, the release points should be no more than 40 m apart for a quick and homogeneous colonization of the area treated.
Highlights
Knowledge of the mobility and dispersal capacity of entomophagous arthropods is essential for the implementation of biological control strategies
The flight range of the parasitoid was evaluated, for 35 days after the release, on 16 trees per each plot, located at 20 and 40 m from the central release point using yellow sticky traps activated with Aonidiella aurantii (Maskell) (Hemiptera: Diaspididae) sexual pheromone and by monitoring the percentage parasitism of the scale on fruits and twigs
The trial was carried out in June–July 2007 in a citrus orchard under integrated pest management located at Lentini (37°20 ́34 ̋N; 14°49 ́44 ̋E) at 80 m above sea level, where no chemical treatments had been applied for three years prior to the trial
Summary
Knowledge of the mobility and dispersal capacity of entomophagous arthropods is essential for the implementation of biological control strategies. In augmentative programs, when the aim is a quick effect of a mass release of natural enemies rather than their establishment, beneficials must move from the release points and spread throughout the infested area (Corbett & Rosenheim, 1996). In addition to having a knowledge of the dispersal abilities of biocontrol agents it is important to know how effective they are at recolonizing crops from untreated surroundings after planting or harvesting and especially after pesticide applications (Desneux et al, 2005, 2007; Langhof et al, 2005). Despite the importance of the distribution of natural enemies for biological control, there are few studies on the dispersal behaviour of biocontrol agents, mainly because it is difficult to measure the dispersal ability of small insects (Hougardy & Mills, 2006; Tabone et al, 2010). The techniques used up to now rely on recording parasitism percentage on natural or artificial hosts, capture numbers on sticky traps or on glue-sprayed plants and/or by using mark-recapture (Keller et al, 1985; Corbett & Rosenheim, 1996; Suverkropp et al, 2009; Yu et al, 2009)
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